This application claims the benefit of a Japanese Patent Application No. 2000-167647 filed Jun. 5, 2000, in the Japanese Patent Office, the disclosure of which is hereby incorporated by reference.
1. Field of the Invention
The present invention generally relates to noise analyzing methods and apparatuses and storage media, and more particularly to a noise analyzing method for analyzing noise which may be generated in an electronic circuit when designing the electronic circuit such as a large scale integrated (LSI) circuit, multi-chip module (MCM) and printed circuit board (PCB) by a computer aided design (CAD), and to a noise analyzing apparatus which analyzes the noise by such a noise analyzing method, and to a computer-readable storage medium which stores a program for causing a computer to carry out such a noise analysis.
Recently, noise analysis has become important when designing an electronic circuit, particularly because the size of electronic circuits has decreased considerably and the operation speed of the electronic circuits has increased greatly. Accordingly, there are demands to accurately and quickly analyze the noise which is generated in the electronic circuit, when designing the electronic circuit.
2. Description of the Related Art
Conventionally, various kinds of noise analyzing tools have been proposed to carry out the noise analysis when designing the electronic circuit. The noise analyzing tool carries out the noise analysis and a noise check using a circuit simulator after an assemble design of the electronic circuit is made, so as to determine noise countermeasures for suppressing the noise. The design of the electronic circuit is modified if necessary based on the determined noise countermeasures. After such a design modification, the noise analysis and the noise check are carried out again, and the above described procedure is repeated until the noise falls within a tolerable range.
The noise which is to be mainly considered when designing the electronic circuit includes reflection noise and crosstalk noise. Normally, the reflection noise is generated by a mismatch of an internal resistance of a driver and a characteristic impedance of a transmission line. On the other hand, the crosstalk noise greatly depends on signal transmitting directions, driving capacity of the driver, a gap between adjacent patterns, and the like. Usually, the crosstalk analysis requires information related to the adjacent patterns, and for this reason, the noise analysis and the noise check are carried out after the assemble design of the electronic circuit is made, using design data. The information related to the adjacent patterns include a pattern gap, a distance for which the patterns run parallel to each other, a position where the patterns are parallel on the transmission lines, and the like.
However, as will be described hereunder, the conventional noise analyzing method does not specify a signal transmitting direction when carrying out the noise analysis of a bus.
FIG. 1 is a diagram for explaining the noise analysis for a case where three bidirectional nets exist. A net refers to a portion which is made up of at least one target circuit element when designing the electronic circuit. For example, when observing a transmission signal waveform between a driver/receiver C and a receiver/driver D (hereinafter referred to as an interval C-D), it is necessary to take into consideration the crosstalk noise of the adjacent nets, that is, a transmission signal waveform between a driver/receiver A and a receiver/driver B (hereinafter referred to as an interval A-B) and a transmission signal waveform between a driver/receiver E and a receiver/driver F (hereinafter referred to as an interval E-F).
In this case, with respect to a transmitting direction Cxe2x86x92D indicated by {circle around (1)}, it is necessary to analyze the crosstalk noise for the interval A-B by taking into consideration a transmitting direction Axe2x86x92B and a transmitting direction Bxe2x86x92A. In addition, with respect to a transmitting direction Dxe2x86x92C indicated by {circle around (2)}, it is necessary to analyze the crosstalk noise for the interval A-B by taking into consideration the transmitting direction Axe2x86x92B and the transmitting direction Bxe2x86x92A. Similarly, it is necessary to analyze the crosstalk noise for the interval E-F by taking into consideration a transmitting direction Exe2x86x92F and the transmitting direction Fxe2x86x92E.
For this reason, it takes an extremely long time to carry out the noise analysis when a large number of adjacent wirings exist. Moreover, the transmitting directions such as Bxe2x86x92A and Fxe2x86x92E are opposite to the transmitting direction Cxe2x86x92D, and the crosstalk noise caused by such a transmission in the opposite direction is particularly large.
For example, if the transmitting direction is always the same between the interval C-D and the interval E-F, the transmitting direction Fxe2x86x92E does not exist with respect to the transmitting direction Cxe2x86x92D. In this case, it is unnecessary and useless to carry out the noise analysis in the transmitting direction Fxe2x86x92E. Such an unnecessary noise analysis not only increases the noise analyzing time, but would obtain an erroneous noise analysis result which indicates that the noise generated is much larger than the crosstalk noise which is would actually be generated.
In other words, because the conventional noise analyzing method does not specify the signal transmitting direction when carrying out the noise analysis of the bus, there was a problem in that the noise analysis is also carried out for combinations of signals which are actually not transmitted, when analyzing the crosstalk of bidirectional signals. Consequently, the conventional noise analyzing method carries out an unnecessary noise analysis, the noise analyzing time is considerably increased thereby. In addition, the conventional noise analyzing method obtains an erroneous noise analysis result which indicates that the noise generated is much larger than the crosstalk noise which is would actually be generated.
Accordingly, it is a general object of the present invention to provide a novel and useful noise analyzing method and apparatus and computer-readable storage medium, in which the problems described above are eliminated.
Another and more specific object of the present invention is to provide a noise analyzing method and apparatus and computer-readable storage medium, which can reduce a noise analyzing time and obtain an accurate noise analysis result, by preventing an unnecessary noise analysis to be carried out for combinations of signals which are actually not transmitted.
Still another object of the present invention is to provide a noise analyzing method comprising analyzing a crosstalk noise based on circuit data in which buses having the same signal transmitting direction and buses having opposite signal transmitting directions are distinguished from each other, by analyzing the crosstalk noise only for the same signal transmitting direction with respect to the buses having the same signal transmitting direction. According to the noise analyzing method of the present invention, it is possible to reduce a noise analyzing time and obtain an accurate noise analysis result, by preventing an unnecessary noise analysis to be carried out for combinations of signals which are actually not transmitted.
A further object of the present invention is to provide a noise analyzing apparatus comprising an analyzing section analyzing a crosstalk noise based on circuit data in which buses having the same signal transmitting direction and buses having opposite signal transmitting directions are distinguished from each other, by analyzing the crosstalk noise only for the same signal transmitting direction with respect to the buses having the same signal transmitting direction. According to the noise analyzing apparatus of the present invention, it is possible to reduce a noise analyzing time and obtain an accurate noise analysis result, by preventing an unnecessary noise analysis to be carried out for combinations of signals which are actually not transmitted.
Another object of the present invention is to provide a computer-readable storage medium which stores a program for causing a computer to carry out a noise analyzing process, where the program comprises the procedure of causing the computer to analyze a crosstalk noise based on circuit data in which buses having the same signal transmitting direction and buses having opposite signal transmitting directions are distinguished from each other, by analyzing the crosstalk noise only for the same signal transmitting direction with respect to the buses having the same signal transmitting direction. According to the computer-readable storage medium of the present invention, it is possible to reduce a noise analyzing time and obtain an accurate noise analysis result, by preventing an unnecessary noise analysis to be carried out for combinations of signals which are actually not transmitted.
Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.